1 . Technical Field
The present invention relates to an electro-optical device using an electro-optical material such as a liquid crystal, a method of driving the same, and an electronic apparatus.
2 . Related Art
A liquid crystal is known as an electro-optical material that has optical characteristics that are changed by electrical energy. The liquid crystal has transmittance that changes in response to an applied voltage. Liquid crystal devices using the change in transmittance are known. Liquid crystal devices include a plurality of scan lines, a plurality of data lines, and a plurality of pixels provided to correspond to intersections of the scan lines and the data lines. The plurality of pixels has a pixel electrode, an opposite electrode, and a liquid crystal element composed of the liquid crystal which is interposed therebetween.
As a method of digitally driving liquid crystal devices, there is known a sub-field driving method that divides one field into a plurality of sub-fields along a time axis, and in each sub-field, applies an on-voltage or an off-voltage to each pixel in accordance to a gray scale. This method is of changing the effective voltage which offers the voltage to be applied to the liquid crystal is performed not by the voltage level but by the application time of a voltage pulse, to control transmittance of a liquid crystal panel. In the method, the voltage level necessary to drive the liquid crystal is only two values, an on-level and an off-level. In a simple sub-field driving method, the grayscales that are able to be displayed are limited by the number of divided sub-fields.
However, at a constant temperature, the response characteristics of the liquid crystal are such that they have a response speed which quickens in response to the magnitude of electrical field applied to the liquid crystal layer in the transition from a steady state (oriented state). The transition from a state where the electrical field is applied to the liquid crystal layer to the oriented state requires a certain amount of response time. This response time is typically several times longer than the time for which the electrical field is applied to the liquid crystal layer.
Japanese Patent No. 4,023,517 discloses technology that can display a number of grayscales which is the same as or greater than the number of sub-fields by using the rise time and fall time of the liquid crystal.
However, the response time of the liquid crystal changes to a great extent due to the temperature. For this reason, even though a grayscale corresponding to a value of digital data can be accurately minced at a certain temperature, the grayscale that has to be displayed becomes inaccurate if the temperature changes. In some instances, even when the value of digital data becomes large, the reversion of a grayscale may arise where the displayed grayscale becomes dark.